Hello,
Thank you for sharing your story here, it means that you trust this forum, and it means that you seek help here,
I have just read your post, the conclusion I came out with, is that your are tormented,..
I'm not going to dive in how u met that girl, and how fast you liked each other and what made her FEELINGS change in one day and night after only one hang out meeting each other.
I'm not being ironic here neither I'm mocking on u, u are too young and she's younger, and ur body is discovering and still growing, u got so much to pass by and to experience.
I'm going to jump directly to the main point when u said:" how do I stop letting this taking so much effect on me, I want to feel okay if things won't work out...".
Take it from me: Don't build high expectations from this relationship, all the catastrophe in our lives was in being excessive, was in going too far, going too far in love going too far in feelings, in hope, in expectations...
What comes fast goes away faster...
I know u feel stuck, alone, can't do anything without her, everything depends on her, ur happiness depends on her, every happiness depends on something or someone isn't true, and if it is true it is temporary.
U got hurt in ur pride, and in ur masculinity and u think something is wrong with u made her leave, and the story isn't like that, you and her your brain chemistry didn't fit with each other, nothing's wrong with you.
Look! I'm going to be quick and lucid and hope u catch up with me.

There is a genius solution that you need to know, and this solution consists on two marvellous tricks:
1)-The art of letting go.
2)-The law of getting used.
they complete each other like day and night, you would never imagine what can an art and law do when they are mixed together! Miracles!
The art of letting go it is voluntary, and the law of getthing used it is an instinct that is combined in the subconscious, but u can't reach it unless u be open to practice the art of letting go, of forgetting, you have to prepare for it, if you give allowance to
your mind and to your spirit to elaborate the road to it. Then u will be able to get used of living without her,
I know u will get used it is a survival basic instinct installed deep in you, and once u get used of her absence u will be okay, free and happy, you will forget about her by time, slowly...little by little...It's like sleeping!!... you don't know when it comes! neither you know the worlds you would be getting through, then suddenly you wake up with the sunlight wondering when you passed out!!.